Constant Impedance Switch

ABSTRACT

A constant impedance switch dynamically manages switch impedance to eliminate or substantially reduce impedance glitches during switching events by stepping variable impedances through sequences of impedance values. As a result, VSWR may be reduced to or near 1:1, allowing programming and circuitry to be simplified. Switch impedance may be maintained for single and multi-throw switches having variable impedances of any order. Each variable impedance may comprise one or more configurable cells, subcells and elements controlled by thermometer, binary, hybrid or other coding technique.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is related to U.S. patent application Ser. No. 13/539,409, filed Jun. 30, 2012, entitled “Multi-Bit Cell Attenuator,” and U.S. patent application Ser. No. 13,539,406, filed Jun. 30, 2012, entitled “Hybrid-Coding for Improving Transient Switch Response in a Multi-Cell Programmable Apparatus,” which are non-provisional, utility patent applications hereby incorporated by reference in their entireties as if fully set forth herein.

TECHNICAL FIELD

The present invention generally relates to switches. More particularly, the invention relates to constant impedance switches.

BACKGROUND

Electronic switches, such as a single pole multi-throw (SP×T) switch in an integrated circuit, grossly deviate from system characteristic impedance Zo, causing an impedance glitch, when they switch between states. Due to the severe impedance mismatch between system and switch ports during switching, signal reflections result in a high voltage standing wave ratio (VSWR).

In summary, impedance glitches slow down communication performance by temporarily disrupting data transmission and reception, pose reliability issues and cause a myriad of costs. Complex circuitry and/or programming are necessary to address problems caused by these glitches. Impedance glitches increase design, fabrication and operating costs given that the complex circuitry and/or programming consume manpower, die or circuit board area and power.

As an example, a switch may be used to select one of several voltage-controlled oscillators (VCOs) to control the modulating frequency coupled to a system. During switching, the impedance glitch initially load-pulls the VCO being selected, which changes its output frequency and causes the phase locked loop (PLL) to unlock. When this occurs, the system is unable to communicate until the loop recovers. Sophisticated circuitry and/or firmware/software programming development are required to overcome these interruptions. In another example, switching glitches in switched-power amplifiers may be detrimental to performance or even cause damage if sophisticated circuitry and/or programming are insufficient to counteract the glitches.

Thus, there is a need for an electronic switch that eliminates or substantially reduces impedance glitches to maintain constant or substantially constant impedance to improve performance, reliability and reduce manpower, circuitry and operating costs.

SUMMARY

This Summary is provided to introduce concepts in a simplified form. These concepts are described in greater detail below in the sections entitled Detailed Description Of Illustrative Embodiments, Brief Description of the Drawings, Claims, and in the figures. This Summary is not intended to identify key or essential features of the described or claimed subject matter, nor limit the scope thereof.

A constant impedance switch dynamically manages switch impedance to eliminate or substantially reduce impedance glitches during switching events (i.e. state transition) by stepping variable impedances through sequences of impedance values. As a result, VSWR may be reduced to or near 1:1, allowing programming and circuitry to be simplified. Switch impedance may be maintained for single and multi-throw switches having variable impedances of any order. Each variable impedance may comprise one or more configurable transistor cells, subcells and elements controlled by thermometer, binary, hybrid or other coding technique. Variable impedance elements may be resistive, capacitive, inductive or any combination thereof. Impedance elements may comprise stacks of transistors designed to provide specific impedances. Switch impedance performance may be calibrated by adjusting sequence timing and/or thresholds.

Constant impedance switch parameters, such as cell, subcell, elements, step range, subrange, resolution, impedance sequence, number of steps, step values, step increments (e.g. step multiplier or log base), step timing, etc. may be determined by a constant impedance switch design program, e.g., by computer executable instructions, to maintain switch impedance during transitions.

A device in accordance with an embodiment of the invention may comprise, for example, a switch configured to maintain switch impedance during switching events by stepping variable impedances through impedance sequences. A method in accordance with an embodiment of the invention may comprise, for example, maintaining impedances of a switch during switch events by stepping variable impedances through sequences of impedance values.

BRIEF DESCRIPTION OF THE DRAWINGS

The foregoing summary, as well as the following detailed description, is better understood when read in conjunction with the accompanying drawings. The accompanying drawings, which are incorporated herein and form part of the specification, illustrate a plurality of embodiments of the present invention and, together with the description, further serve to explain the principles involved and to enable a person skilled in the relevant art(s) to make and use the disclosed technologies. However, embodiments of the invention are not limited to the specific implementations disclosed herein. Each figure represents a different embodiment and components in each embodiment are intentionally numbered differently compared to potentially similar components in other embodiments.

FIG. 1 illustrates an exemplary constant impedance switch with constant impedance control in accordance with an embodiment of the invention.

FIG. 2 illustrates a block diagram of an exemplary constant impedance single pole double throw first order switch with a plurality of variable impedances configured to provide constant impedance in accordance with an embodiment of the invention.

FIG. 3 illustrates an equivalent circuit of the exemplary constant impedance switch in FIG. 2 in accordance with an embodiment of the invention.

FIG. 4 illustrates an exemplary configurable transistor cell implementation of variable impedances in accordance with an embodiment of the invention.

FIG. 5 illustrates an exemplary implementation of a control circuit to control a constant impedance switch in accordance with an embodiment of the invention.

FIG. 6 illustrates an exemplary implementation of a control circuit to control a constant impedance switch in accordance with an embodiment of the invention.

FIG. 7 illustrates a block diagram of an exemplary constant impedance single pole double throw second order switch with a plurality of variable impedances configured to provide constant impedance in accordance with an embodiment of the invention.

FIG. 8 illustrates an exemplary method in accordance with an embodiment of the invention.

DETAILED DESCRIPTION OF ILLUSTRATIVE EMBODIMENTS

Reference will now be made to embodiments of the invention, examples of which are illustrated in the accompanying drawings. While the technology will be described in conjunction with various embodiments, it will be understood that the embodiments are not intended to limit the present technology. On the contrary, the present technology is intended to cover alternatives, modifications, and equivalents, which may be included within the spirit and scope the various embodiments as defined herein, including by the appended claims. In addition, in the following detailed description, numerous specific details are set forth in order to provide a thorough understanding of the present technology. However, the present technology may be practiced without these specific details. In other instances, well known methods, procedures, components, and circuits have not been described in detail as not to unnecessarily obscure aspects of the embodiments presented.

References in the specification to “embodiment,” “example embodiment,” or the like, indicate that the embodiment described may include a particular feature, structure, characteristic or step, but every embodiment may not necessarily include the particular feature, structure, characteristic or step. Moreover, such phrases are not necessarily referring to the same embodiment. Furthermore, when a particular feature, structure, or characteristic is described in connection with an embodiment, it is submitted that it is within the knowledge of one skilled in the art to implement such feature, structure, or characteristic in connection with other embodiments whether or not explicitly described.

Unless specifically stated otherwise, terms such as “sampling,” “latching,” “determining,” “selecting” “storing,” “registering,” “creating,” “including,” “comparing,” “receiving,” “providing,” “generating,” “associating,” and “arranging”, or the like, refer to the actions and processes of an electronic device that manipulates and transforms data represented as physical (electronic) quantities within the electronic device. The terms “logic,” “function,” “step,” and the like refer to functionality that may be implemented by hardware (digital and/or analog) or a combination of hardware, software and/or firmware. Unless specifically indicated, described and claimed functionality may be implemented by hardware (digital and/or analog) or a combination of hardware, software and/or firmware. The term “programmable” and the like refer to functionality permitting definition or selection of functionality to vary performance of logic from one embodiment to the next, whether one-time or any number of times such as by reprogrammable functionality. Logic may be referred to as being enabled, disabled, high, low, on, off and the like.

Certain terms are used throughout the following description and claims to refer to particular system components and configurations. As one skilled in the art will appreciate, various skilled artisans and companies may refer to a component by different names. The discussion of embodiments is not intended to distinguish between components that differ in name but not function. In the following discussion and in the claims, the terms “including” and “comprising” are used in an open-ended fashion, and thus should be interpreted to mean “including, but not limited to . . . .” Also, the term “couple” or “couples” is intended to mean either an indirect or direct electrical connection. Thus, if a first device couples to a second device, that connection may be through a direct electrical connection or through an indirect electrical connection via other devices and connections. Furthermore, the term “information” is intended to refer to any data, instructions, or control sequences that may be communicated between components of a device. For example, if information is sent between two components, data, instructions, control sequences, or any combination thereof may be sent between the two components. The terms constant, substantially constant, maintain and substantially maintain are used interchangeably to have the same meaning Maintenance of an impedance value permits some variation from the impedance value, but considerably less variation than impedance glitches during normal switching.

A constant impedance switch dynamically manages switch impedance to eliminate or substantially reduce impedance glitches during switching events (i.e. state transition) by stepping variable impedances through sequences of impedance values. As a result, VSWR may be reduced to or near 1:1, allowing programming and circuitry to be simplified. Switch impedance may be maintained for single and multi-throw switches having variable impedances of any order. Each variable impedance may comprise one or more configurable transistor cells, subcells and elements controlled by thermometer, binary, hybrid or other coding technique. Variable impedance elements may be resistive, capacitive, inductive or any combination thereof. Impedance elements may comprise stacks of transistors designed to provide specific impedances. Switch impedance performance may be calibrated by adjusting sequence timing and/or thresholds.

Constant impedance switch parameters, such as cell, subcell, elements, step range, subrange, resolution, impedance sequence, number of steps, step values, step increments (e.g. step multiplier or log base), step timing, etc. may be determined by a constant impedance switch design program, e.g., by computer executable instructions, to maintain switch impedance during transitions.

A device in accordance with an embodiment of the invention may comprise, for example, a switch configured to maintain switch impedance during switching events by stepping variable impedances through impedance sequences. A method in accordance with an embodiment of the invention may comprise, for example, maintaining impedances of a switch during switch events by stepping variable impedances through sequences of impedance values.

Steps may be linear, logarithmic or other uniform or non-uniform increment to substantially maintain impedance during state transitions. Depending on each particular state transition, each variable impedance may be fixed or step through a sequence. Impedance configurations and sequence parameters may be the same or different for each variable impedance. For example, in a bidirectional switch where each port couples to a shunt impedance and each path (or arm) has a series impedance, sequences for one transition may be reversed for another transition, resulting in similar impedance cell configurations control. Switch impedance control may be implemented in digital and/or analog hardware, firmware and/or software. A sequence of control signals may be generated to step the at least one variable impedance through sequence(s) of impedance values for one or more switch events.

Each cell having one or more subcells or elements may provide an impedance range or subrange (if there are multiple cells) and each subcell having one or more elements may provide a subrange of impedance. Each impedance range, subrange and step may be uniform or nonuniform. Various cells and subcells may be fixed or variable with at least one cell being variable. Each variable cell or variable subcell comprises a plurality of stages, which may also be referred to as steps. Each unit cell (i.e. element) has a unit value or step value. The range or subrange of each variable cell or subcell is determined by the number of unit cells and their unit/step values therein. Stages or steps may be formed by physical combinations or single elements selected in the alternative with physical separation between distinct unit cells or stages. Regardless of the cellular architecture, the plurality of cells, subcells and elements serve to step one or more impedance parameters.

One or more cells may have a bypass to bypass or disable a cell. For example, a bypass may pass a signal through a cell without modification, although perhaps with some insertion loss. An advantage of variable cells is that a plurality of steps may share a single bypass, thereby reducing insertion loss by reducing the number of cells.

For variable cells, there are two perspectives to consider, intra-cell and inter-cell when considering architecture, coupling, coding, etc. within or between cells. Intra-cell stages or subcells, may be coupled in serial, parallel, a combination thereof or other configurations. Inter-cell coupling that externally couples cells may be serial, parallel, a combination thereof or other configurations.

Intra-cell and inter-cell coding may depend on the cell architecture. Intra-cell coding in variable cells may be the same or different amongst variable cells. Some variable cells may be thermometer-coded while others may be binary-coded while still others may have other coding. Inter-cell coding of cells in a step device may be the same or different compared to intra-cell coding of variable cells. A control code may be decoded, e.g., using a map or table, to translate a compact code to control selection of fixed and variable cells according to a desired state of the step device.

In some embodiments, direct control of cells may be implemented with control codes. In other embodiments, compact control codes and decoding may be used to generate inter-cell and intra-cell control codes. Direct or indirect control may be implemented in many ways. For example, logic may be incorporated into cells and/or into a step device external to cells, e.g., intra-cell logic and/or inter-cell logic. Decoding may be implemented in many ways, e.g., intra-cell logic and/or inter-cell logic implemented in analog or digital hardware or a combination of hardware and software, such as gates, multiplexer, translation table or map, etc. Each device state may be associated with a set of cell states and signals that would cause the enablement and disablement of different subcells or elements in the cells to generate the selected state for each cell. Each selectable cell, subcell, element and step within a cell may be implemented by any selectable technique. In some embodiments, elements in each cell or step within a cell may be implemented as one or more selectable transistor (e.g. FET) switches that enable and disable or couple and decouple components in a cell, whether the cell is a single or a multi-cell, in accordance with the desired cell state. The components, e.g., resistors, may be fixed or variable. In other embodiments, transistors may be impedance elements that switch themselves in and out of a circuit, designed to provide particular impedances when ON and OFF.

FIG. 1 illustrates an exemplary constant impedance switch with constant impedance control in accordance with an embodiment of the invention. Switch 100 represents a single pole double throw (SPDT or 1P2T) switch, although embodiments may be implemented in any switch having any number of poles and throws to maintain impedance during switching. Switch 100 and other constant impedance switches may be unidirectional or bidirectional. Switch 100 is shown as a radio frequency RF switch, although embodiments may be implemented in any technology. Switch 100 has three ports, first port RF1, second port RF2 and common or third port RFCOM. Common port RFCOM comprises the single pole while first and second ports RF1, RF2 comprise first and second throws.

Control CTRL specifies the states, and transitions, of switch 100. Switch 100 is shown in a center OFF or open position or state. Other embodiments may or may not have an all OFF state. Control CTRL may couple common port RFCOM to first port RF1, enabling a first path in a conducting or ON state. Control CTRL may couple common port RFCOM to second port RF2, enabling a second path in a conducting or ON state. Thus, in this embodiment there are three static states or conditions: the OFF (all paths off) or open state, a first path ON and second path OFF state and a second path ON first path OFF state. Six transitions between states (dynamic conditions) include open state to the first path state and vice versa, open state to the second path state and vice versa and the first path state to the second path state and vice versa.

Switch 100 may be implemented using a plurality of variable impedances. One or more variable impedances in each path of a switch may shift between high and low impedances depending on the state transition. A high impedance may provide the equivalent of an open circuit or OFF state while a low impedance may provide the equivalent of a short circuit or ON state for a path. Instead of abrupt changes in impedance that cause impedance glitches, state transitions are accomplished by concurrently stepping multiple variable impedances in concert to substantially maintain impedance looking into one or more ports RF1, RF2, RFCOM at system characteristic impedance Zo. This may be accomplished with a certain number of impedance steps while preserving normal switch time without the impedance steps. The number of steps, step sizes and other details may vary between applications and requirements. As but one of many examples, a one microsecond (μs) switch time can be preserved while reducing VSWR during switching from more than 9:1 down to 1.3:1.

FIG. 2 illustrates a block diagram of an exemplary constant impedance single pole double throw first order switch with a plurality of variable impedances configured to provide constant impedance in accordance with an embodiment of the invention. Constant impedance switch 200 may be implemented in a variety of ways. In the embodiment shown, SPDT switch 200 comprises first variable series impedance ZS1 and first variable shunt impedance ZP1 coupled in a first path between first port RF1 and common port RFCOM. Switch 200 also comprises second variable series impedance ZS2 and second variable shunt impedance ZP2 coupled in a second path between second port RF2 and common port RFCOM. Finally, switch 200 comprises third variable shunt impedance ZP3 coupled to third or common port RFCOM. Third variable shunt impedance ZP3 may be viewed as being coupled in both the first and second paths. Each variable impedance ZS1, ZP1, ZS2, ZP2, ZP3 may comprise any impedance elements or components, whether resistive, capacitive, inductive or any combination thereof.

A controller (not shown) provides control signals CTRL to control first variable series impedance ZS1, first variable shunt impedance ZP1, second variable series impedance ZS2, second variable shunt impedance ZP2 and third variable shunt impedance ZP3. Control CTRL may step or hold variable impedances depending on which state transition is occurring. By controlling each variable impedance ZS1, ZP1, ZS2, ZP2, ZP3, control CTRL can place switch 200 in each of its three static states by transitioning through any of the six dynamic conditions between the three static states while maintaining substantially constant impedance at first, second and third ports RF1, RF2, RFCOM. Each variable impedance ZS1, ZP1, ZS2, ZP2, ZP3 has static and dynamic (e.g. stepped) values to maintain constant impedance at first, second and third ports RF1, RF2, RFCOM.

FIG. 3 illustrates an equivalent circuit of the exemplary constant impedance switch in FIG. 2 in accordance with an embodiment of the invention. As illustrated in FIG. 3, switch 300 is deployed in a system having characteristic impedance Zo. Note that characteristic impedance Zo may be the same or different at each port RF1, RF2, RFCOM, but for purposes of discussion is presumed to be the same. When the impedance looking into each port RF1, RF2, RFCOM is the same as system characteristic impedance Zo, then there will be no impedance glitches and VSWR at each port will be 1:1. The impedance of switch 300 looking into first port RF1 is given by first port impedance Z1. The impedance of switch 300 looking into second port RF2 is given by second port impedance Z2. The impedance of switch 300 looking into third port RF3 is given by third port impedance Z3. A design and operation objective is to control each variable impedance ZS1, ZP1, ZS2, ZP2, ZP3 to substantially maintain each port impedance Z1, Z2 and Z3 at system characteristic impedance Zo during both static states and dynamic conditions (transitions) between states.

Determining how to control each impedance ZS1, ZP1, ZS2, ZP2, ZP3 to maintain impedance at each port RF1, RF2 and RFCOM requires an impedance analyses to solve for variables. When characteristic impedance Zo is the same for each port RF1, RF2 and RFCOM, the number of static states and dynamic conditions may be reduced due to symmetry. Static states can be reduced to two states: an open (OFF) state and a path (either path) ON state. Dynamic conditions can also be reduced to two conditions: switching between an OFF state and a path ON state and switching between path ON states (i.e. from first path ON, second path OFF state to first path OFF, second path ON state and vice versa).

In a first dynamic condition when switching between an OFF state and a path ON state, one or the other of the first and second paths will be OFF, which means one of first and second variable series impedances Zs1, Zs2 are deemed infinite (open circuit). For purposes of calculations, assume the first path is ON and the second path is OFF, which would mean for purposes of calculations that second variable series impedance Zs2 is an ideal high impedance. With second variable series impedance Zs2 open, second variable series impedance Zs2 and second variable shunt impedance Zp2 are irrelevant to the calculation of first and third port impedances Z1 and Z3. First port impedance Z1 is given by Equation 1:

Z ₁ =Z _(p3)∥[(Z _(o) ∥Z _(p1))+Z _(s1)]  Equation 1

When second variable series impedance Zs2 is open, second port impedance Z2 equals second variable shunt impedance Zp2. In order for second port impedance Z2 to be equal to characteristic impedance Zo, second variable shunt impedance Zp2 must be equal to characteristic impedance Zo. Thus, second port impedance Z2 is given by Equation 2:

Z₂=Z_(p2)=Z_(o)   Equation 2

Given the remaining circuit comprising first variable series impedance Zs1 and first and third variable shunt impedances Zp1, Zp3, symmetry in this circuit means first and third variable shunt impedances Zp1, Zp3 will be the same, as will first and third port impedances Z1 and Z3. Thus, third port impedance Z3 is given by Equation 3:

Z₃=Z₁   Equation 3

Characteristic impedance Zo is known since it is defined by the system that switch 300 is coupled to. Given that system characteristic impedance Zo is known, the only variables left are first variable series impedance Zs1 and first variable shunt impedance Zp1. These variables may be selected so that first port impedance Z1 equals characteristic impedance Zo. Assuming that step values for first variable series impedance Zs1 are selected, step values for first variable shunt impedance Zp1 may be determined by solving the equation for first variable shunt impedance Zp1, which is given by Equation 4:

$\begin{matrix} {Z_{p\; 1} = \frac{{2\; Z_{o}^{2}} \pm \sqrt{{4\; Z_{o}^{4}} + {4\; Z_{o}^{2}Z_{s\; 1}}}}{2\; Z_{s\; 1}}} & {{Equation}\mspace{14mu} 4} \end{matrix}$

In one example, characteristic impedance Zo is 50Ω. The value of first variable series impedance Zs1 in a first path ON state (static state) may be dependent on an insertion loss requirement for an application of the switch. In this example, a static ON value of 1.25Ω may be selected as the static ON value of first variable series impedance Zs1. A static OFF value may also be selected for first variable series impedance Zs1 based on a requirement for an application of the switch. For example, a static OFF value of 10 kΩ may be selected as the static OFF value of first variable series impedance Zs1. A lower limit may also be selected for the shunt branch. For example, 50Ω may be the lower limit when the shunt branch is on. The number of steps or increments of variable impedances may also be selected. For example, one embodiment may have 10 steps η while other embodiments may have 5, 8, 15 or other number of steps. The type of transition across the step range may also be selected. For example, the type of transition may be linear, nonlinear, logarithmic, exponential, etc.

Table 1 below illustrates an example using a linear impedance step to maintain first, second and third port impedances Z1, Z2, Z3 at 50Ω during a transition from a first path ON state, second path OFF state to an all OFF state. In this embodiment, the uniform, linear step of first variable series impedance Zs1 is 499.875Ω. Equation 4 provides the necessary value for first variable shunt impedance Zp1 based on the selected step value for first variable series impedance Zs1. It may be observed that this results in the vast majority of the impedance step for first variable shunt impedance Vp1 occurring in the first step (η=1) from 5 kΩ to 55.2Ω. While a linear step may substantially eliminate impedance glitches in some embodiments, in this example there may be an impedance glitch. Other embodiments using a uniform, linear step may not result in such a large change in step magnitude (i.e. step size) based on design parameters and/or may permit a larger number of steps to reduce the step size (i.e. increase resolution). Other embodiments may use nonlinear (e.g. logarithmic or fixed multiple, variable multiple) steps or a mixture of linear and nonlinear steps (i.e. mixed or hybrid steps).

TABLE 1 Linear Impedance Step for Path 1 ON to all OFF η Z_(s1) Z_(p1) Z₁ Z₂ Z₃ 1.25 5000.00 50.25 50.00 50.25 1 501.13 55.20 50.00 50.00 50.00 2 1001.00 52.60 50.00 50.00 50.00 3 1500.88 51.70 50.00 50.00 50.00 4 2000.75 51.30 50.00 50.00 50.00 5 2500.63 51.00 50.00 50.00 50.00 6 3000.50 50.80 50.00 50.00 50.00 7 3500.38 50.70 50.00 50.00 50.00 8 4000.25 50.60 50.00 50.00 50.00 9 4500.13 50.60 50.00 50.00 50.00 10 5000.00 50.50 50.00 50.00 50.00

Table 2 below illustrates an example using a logarithmic impedance step to maintain first, second and third port impedances Z1, Z2, Z3 at 50Ω during a transition from a first path ON state, second path OFF state to an all OFF state. The logarithmic base selected in this embodiment is 2.2. A number of factors may be evaluated to determine the most appropriate base, including the characteristic impedance, impedance range, power handling requirements, operating frequency range, etc. For example, in an RF implementation, the first step of 3187.20Ω from 5 kΩ to 1813.80Ω for first variable shunt impedance Zp1 is an acceptable step in view of 50Ω characteristic impedance. Each step η is the exponent the base is raised to, which increases the multiple applied to static first variable series impedance Zs1 in each step η. Equation 4 provides the necessary value for first variable shunt impedance Zp1 based on the selected step value for first variable series impedance Zs1. It may be observed that the logarithmic steps result in a more gradual sweep in impedance values for first variable series impedance Zs1 and first variable shunt impedance Vp1. This avoids substantial impedance spikes, resulting in a VSWR of nearly 1:1 during switching transitions. It may also be observed from Table 2 that, at least in some embodiments, fewer steps may be used, VSWR design specifications permitting. Other embodiments may require higher resolution, which may require additional steps depending on the linearity of steps permitted to remain within design specifications.

TABLE 2 Logarithmic Impedance Step for Path 1 ON to all OFF η Multiple Z_(s1) Z_(p1 &) Z_(p3) Z₁ Z₂ Z₃ 1.25 5000.00 50.25 50.00 50.25 1 2.20 2.76 1813.80 50.00 50.00 50.00 2 4.84 6.07 826.80 50.00 50.00 50.00 3 10.65 13.35 381.00 50.00 50.00 50.00 4 23.43 29.38 183.80 50.00 50.00 50.00 5 51.54 64.63 101.90 50.00 50.00 50.00 6 113.38 142.18 70.60 50.00 50.00 50.00 7 249.44 312.79 58.60 50.00 50.00 50.00 8 548.76 688.14 53.80 50.00 50.00 50.00 9 1207.27 1513.92 51.70 50.00 50.00 50.00 10 2655.99 5000.00 50.50 50.00 50.00 50.00

The results found in the first dynamic condition may be used to solve equations in other dynamic conditions. In the second dynamic condition when switching between path ON states (i.e. from first path ON, second path OFF state to first path OFF, second path ON state and vice versa), third variable shunt impedance Zp3 is infinite (open circuit). This leaves four variables to control: first and second series impedances Zs1, Zs2 and first and second variable shunt impedances Zp1, Zp2. First port impedance Z1 is given by Equation 5, second port impedance Z2 is given by Equation 6 and third port impedance Z3 is given by Equation 7:

Z ₁={[(Zo∥Zp2)+Zs2]∥Zo+Zs1}∥Zp1   Equation 5

Z ₂={[(Zo∥Zp1)+Zs1]∥Zo+Zs2}∥Zp2   Equation 6

Z ₃=[(Z _(o) ∥Z _(p1))+Z _(s1)]∥[(Z _(o) ∥Z _(p2))+Z _(s2)]  Equation 5

Equations 5-7 can be solved for any variable. In Equations 5-7, characteristic impedance Zo is known (e.g. 50Ω) since it is defined by the system switch 300 is coupled to. In some embodiments, it may be desirable to ensure that the solutions for each transition utilize the same set of step values (albeit in different orders as needed to maintain port impedances) to minimize design, fabrication and operating costs. Other embodiments may employ different sets of step values for different transitions. However, for purposes of this embodiment, it will be presumed that the same set of step values will be used for all transitions (in different orders as needed to maintain port impedances). Thus, the information (step sequences) in Table 2 for first variable series impedance Zs1 and first variable shunt impedance Zp1 could be used and, due to symmetry, could be reversed for second variable series impedance Zs2 and second variable shunt impedance Zp2.

Table 3 below shows a slightly different logarithmic step example than shown in Table 2 to maintain first, second and third port impedances Z1, Z2, Z3 at 50Ω during a transition from a first path ON state, second path OFF state to second path ON state, first path OFF state. In the embodiment shown in Table 3, the log base is 2.16 and the static ON impedance is 1.4Ω for first variable series impedance Zs1. The static OFF value remains 10 kΩ. Characteristic impedance Zo remains at 50Ω. The number of steps η remains at 10. The sets of step values (step sequences) in Table 3 for first variable series impedance Zs1 and first variable shunt impedance Zp1 were verified for the first path ON to all OFF state transition. The step sequences can be reused in the first path ON to second path ON state transition. Due to symmetry, the step sequences for first variable series impedance Zs1 and first variable shunt impedance Zp1 are reversed for second variable series impedance Zs2 and second variable shunt impedance Zp2.

TABLE 3 Logarithmic Impedance Step for Path 1 ON to Path 2 ON Multi- η ple Z_(s1) Z_(p1) Z_(s2) Z_(p2) Z₁ Z₂ Z₃ 1.4 5000.0 5000.0 50.5 50.00 50.00 50.00 1 2.16 3.1 1609.1 1473.8 51.7 50.00 50.00 50.00 2 4.67 6.7 747.6 682.3 53.8 50.00 50.00 50.00 3 10.08 14.5 351.7 315.9 58.5 50.00 50.00 50.00 4 21.77 31.3 173.9 146.2 69.9 50.00 50.00 50.00 5 47.02 67.7 99.1 67.7 99.1 50.00 50.00 50.00 6 101.56 146.2 69.9 31.3 173.9 50.00 50.00 50.00 7 219.37 315.9 58.5 14.5 351.7 50.00 50.00 50.00 8 473.83 682.3 53.8 6.7 747.6 50.00 50.00 50.00 9 1023.49 1473.8 51.7 3.1 1609.1 50.00 50.00 50.00 10 2210.74 5000.0 50.5 1.4 5000.0 50.00 50.00 50.00

The foregoing equations for this embodiment and equations for other embodiments of a constant impedance switch can be solved by a switch design calculator, which may be implemented as software instructions stored on a computer-readable storage medium and executed by a computer processor. Such a calculator can simultaneously, including iteratively, solve (e.g. try to find an optimal value) for each variable impedance based on a selected design parameters provided to the calculator, such as one or more of impedance step range, resolution, switch time, impedance type or implementation, number of steps, characteristic impedance, log base, insertion loss, isolation. The calculator can solve for one, several or all state transitions for a particular switch.

There are numerous advantages to substantially maintaining first, second and port impedances Z1, Z2, Z3 at characteristic impedance Zo during each of its transitions. By maintaining switch impedance during transitions, VSWR remains at or near 1:1, impedance spikes and reflections are eliminated, switching time may be reduced, operations can continue without delay and there is no need to design, fabricate and operate complex circuitry and programming to contend with impedance spikes and reflections.

FIG. 4 illustrates an exemplary configurable transistor cell implementation of variable impedances in the exemplary constant impedance switch in FIG. 2 in accordance with an embodiment of the invention. Constant impedance switch 400 comprises first variable series impedance cell ZS1 c, first variable shunt impedance cell ZP1 c, second variable series impedance cell ZS2 c, second variable shunt impedance cell ZP2 c and third variable shunt impedance cell ZP3 c. Each variable impedance in this embodiment is shown as one cell with selectable subcells having sets of selectable elements, such that each cell, subcell and its elements are used in each transition. In other embodiments, each variable impedance may comprise any number of cells, subcells and elements. In some embodiments, different cells, different sets of subcells within cells and/or different sets of transistors in subcells or cells may be selectable for different transitions or operating conditions (power, voltage, etc.). For example, a multiplexer may be deployed to select among cells and/or subcells.

Impedance cell architecture may vary widely between embodiments. In some embodiments, each variable impedance may comprise one or more cells, each cell may comprise a plurality of subcells and each subcell may comprise elements. Cells, subcells and elements may be used in the alternative or in combination. A cell may also comprise elements with or without subcells. Selectable elements may comprise any type(s) of impedance. Examples of elements include, without limitation, resistors, inductors, capacitors, pin diodes and transistors. In this embodiment, the elements are transistors. Depending on the architecture, elements may be individually selectable or selectable by selecting subcells or cells. However configured, elements are selected or configured, in any order and combination, to provide the impedance values in impedance sequences, such as the impedance sequences shown in Table 3. Each selected configuration of cells, subcells and elements provides an impedance that can be utilized to provide all or part of one or more step values in an impedance sequence. Cells, subcells and elements may be configured for combination using any arithmetic operation(s), e.g., addition, subtraction, multiplication, division. For example, it may be observed that subcells shown in FIG. 4 are in parallel. In other embodiments, subcells may be arranged in serial and/or parallel. In some embodiments only one subcell is selected (ON) for each step in a sequence. In other embodiments, a subcell is added or subtracted in each sequence, such that all subcells would be on in the first step or the last step of a sequence. In other embodiments, subcells are selected individually or grouped to provide certain impedance values in a sequence without selecting all at once.

In this embodiment, first variable series impedance cell ZS1 c comprises a plurality of subcells Zs1 a . . . ZS1 n. First variable shunt impedance cell Zp1 c comprises a plurality of subcells Zp1 a . . . ZP1 n. Second variable series impedance cell ZS2 c comprises a plurality of subcells ZS2 a . . . ZS2 n. Second variable shunt impedance cell ZP2 c comprises a plurality of subcells ZP2 a . . . ZP2 n. Third variable shunt impedance cell ZP3 c comprises a plurality of subcells ZP3 a . . . ZP3 n. The letter “a” represents a first subcell and the letter “n” represents any number. There may be any number of subcells between a and n subcells. The subcells are selected, in any order and combination, to configure the impedance values in an impedance sequence, such as the impedance sequences shown in Table 3.

Each subcell may comprise one or more selectable impedance elements. In this embodiment, selectable impedance elements comprise transistors and, specifically, MOSFETs. In this embodiment, each subcell comprises a set or stack of three selectable transistors. However, in other embodiments there may be any number of elements (e.g. transistors). The number of transistors in respective cells or respective subcells may be the same or different. In some embodiments, power handling, isolation, insertion loss and/or other design parameters may necessitate multiple transistors.

Subcell ZS1 a comprises first transistors M1. Subcell ZS1 n comprises second transistors M2. Subcell Zp1 a comprises third transistors M3. Subcell ZP1 n comprises fourth transistors M4. Subcell ZS2 a comprises fifth transistors M5. Subcell ZS2 n comprises sixth transistors M6. Subcell ZP2 a comprises seventh transistors M7. Subcell ZP2 n comprises eight transistors M8. Subcell ZP3 a comprises ninth transistors M9. Subcell ZP3 n comprises tenth transistors M10.

First resistors R1 coupled to the gates of first transistors M1 together establish a first RC time constant defining switching speed for subcell Zs1 a in response to control signal Vs1 a. Second resistors R2 coupled to the gates of second transistors M2 together establish a second RC time constant defining switching speed for subcell Zs1 n in response to control signal Vs1 n. Third resistors R3 coupled to the gates of third transistors M3 together establish a third RC time constant defining switching speed for subcell ZP1 a in response to control signal Vp1 a. Fourth resistors R4 coupled to the gates of fourth transistors M4 together establish a fourth RC time constant defining switching speed for subcell ZP1 n in response to control signal Vp1 n. Fifth resistors R5 coupled to the gates of fifth transistors M5 together establish a fifth RC time constant defining switching speed for subcell ZS2 a in response to control signal Vs2 a. Sixth resistors R6 coupled to the gates of sixth transistors M6 together establish a sixth RC time constant defining switching speed for subcell ZS2 n in response to control signal Vs2 n. Seventh resistors R7 coupled to the gates of seventh transistors M7 together establish a seventh RC time constant defining switching speed for subcell ZP2 a in response to control signal Vp2 a. Eighth resistors R8 coupled to the gates of eighth transistors M8 together establish an eighth RC time constant defining switching speed for subcell ZP2 n in response to control signal Vp2 n. Ninth resistors R9 coupled to the gates of ninth transistors M9 together establish a ninth RC time constant defining switching speed for subcell ZP3 a in response to control signal Vp3 a. Tenth resistors R10 coupled to the gates of tenth transistors M10 together establish a tenth RC time constant defining switching speed for subcell ZP3 n in response to control signal Vp3 n. Of course there may be additional subcells between cells a and n, each comprising additional impedance elements (e.g. transistors) configured to provide specific impedances. Also note that transistor bias is not shown, but may be necessary in some embodiments.

Although constant impedance switch 400 is shown as non-absorptive, constant impedance switches in other embodiments may be absorptive. In an absorptive switch, each shunt impedance subcell is coupled to ground through an impedance (e.g. resistor), which reduces the impedance that shunt cells must provide.

Table 4 provides an exemplary implementation of part of the switch shown in FIG. 4 with respect to the sequences provided in Table 2 to transition from the Path 1 ON, path 2 OFF state to the all paths OFF state. The parameters in Table 4 are based on a transistor stack height in each subcell of three, a characteristic impedance of 45 Ohms, a corner frequency f_(o) of 16 MHz and unit Oxide capacitance equal to 1.84 pF/mm. Of course, other embodiments may have the same or different parameters. The switching speed is given by an RC time constant in Equation 8, where capacitance C is the gate capacitance of a particular transistor, e.g., M1, and R is the gate resistor, e.g. R1:

$\begin{matrix} {{RC} = \frac{1}{2\pi \; f_{o}}} & {{Equation}\mspace{14mu} 8} \end{matrix}$

TABLE 4 Subcell Design for Logarithmic Impedance Step for Path 1 ON to all OFF Sequence of Shunt cell turning off Series cell Sequence of turning gate resistor transistors with gate resistor on transistors with values (Ω) in widths (mm) in values (Ω) in widths (mm) in cells cells Zp1a-n η cells Zs1a-n cells Zs1a-n Zp1a-n & Zp3a-n & Zp3a-n 0.80556 (All ON) 6,711 All OFF 1 0.37294 14,496 0.00138 3,914,561 2 0.17266 31,311 0.00169 3,192,357 3 0.07993 67,631 0.00397 1,361,974 4 0.03701 146,084 0.00971 556,474 5 0.01713 315,541 0.02318 233,201 6 0.00793 681,568 0.04668 115,808 7 0.00367 1,472,187 0.07295 74,111 8 0.00170 3,179,925 0.08594 62,903 9 0.00147 3,688,713 0.07568 (All ON) 71,436 10 All OFF 0.07136 75,757

The size of each transistor and the number or stack of transistors in each cell or subcell may be based on a variety of factors. For example, smaller transistor width generally results in higher impedance. Accomplishing the sequence of impedance steps may require different impedances in each cell or subcell. A smaller stack of transistors may reduce insertion loss, but also may decrease isolation and decrease power handling capability. A second order switch may provide better isolation than a first order switch.

While the configuration of FIG. 4 and sequences in Table 4 permit sequence control such that one subcell or element is turned on or off in each step, resulting in all subcells or elements being on or off at the end of a sequence, other embodiments may employ the same or different configurations of cells, subcells, elements and coding to control impedance sequencing during switching. In other embodiments, cells, subcells and elements may be configured for and controlled by thermometer, binary, hybrid or other coding techniques to assemble and disassemble impedances in each step of a sequence. Cell, subcell and element configurations and coding techniques are discussed, for example, in U.S. patent application Ser. No. 13/539,409, filed Jun. 30, 2012, entitled “Multi-Bit Cell Attenuator,” and U.S. patent application Ser. No. 13,539,406, filed Jun. 30, 2012, entitled “Hybrid-Coding for Improving Transient Switch Response in a Multi-Cell Programmable Apparatus,” which are non-provisional, utility patent applications hereby incorporated by reference in their entireties as if fully set forth herein. Techniques discussed in these applications and other techniques may be applied to various embodiments of the technology described herein.

FIG. 5 illustrates an exemplary implementation of a control circuit in accordance with an embodiment of the invention. Control circuit 500 presents one of many possible embodiments to control cells, subcells and elements to provide impedance sequences for state transitions. Control circuit 500 may be used to control the exemplary constant impedance switch in FIG. 2, among other embodiments with appropriate scaling.

Control circuit 500 comprises decoder 505, Z1(a:n) driver 510, Z2(a:n) driver 515 and Z3(a:n) driver 520. Decoder 505 receives state or state transition information in switch control signals V1 and V2, which may be provided, for example, by a switch controller or processor executing instructions. Decoder 505 decodes switch control signals V1, V2 into first, second and third impedance control signals VD1, VD2 and VD3. First impedance control signal VD1 is provided to Z1 driver 510, second impedance control signal VD2 is provided to Z2 driver 515 and third impedance control signal VD3 is provided to Z3 driver 520. First, second and third impedance control signals VD1, VD2 and VD3 may step discretely, e.g. zero to three volts.

In one embodiment, first, second and third impedance control signals VD1, VD2 and VD3 may be used to provide timing between steps in impedance sequences by using RC time constants to slew these control signals. The slewed control signals are compared to thresholds to provide timing for each step in the sequence. For example, if first, second and third impedance control signals are 0 Volt low and 3 Volt high then thresholds may be generated by linearly or nonlinearly dividing 3 Volts by the number of steps in a transition sequence to generate respective thresholds Vth(a:n). As the slewed signals V1 s, V2 s and V3 s cross each respective threshold Vth(a:n) a subcell is activated or deactivated. In other embodiments, independent timing circuitry and other timing techniques may be used to provide timing between sequence steps.

When RC circuits are used to slew impedance control signals, there may be an exponential rise from 0V to Vdd voltage range and an exponential fall from Vdd to 0V. Threshold voltages could be set by unit resistors or different resistors in a resistive ladder. Resistors and threshold levels (i.e. comparator trigger points) may be selected to provide uniform or non-uniform timing between sequence steps. To optimize uniform step timing, thresholds can be adjusted by using different value resistors in the ladder. An array of resistors can be printed into a substrate. In some embodiments, when unit resistors are used, resulting in non-uniform timing between sequence steps, impedance magnitudes in steps may be adjusted for the non-uniform timing to fit a desired impedance transition curve.

In the embodiment shown in FIG. 5, first impedance control signal VD1 is slewed by a time constant provided by first timing resistor R1S and first timing capacitor C1, which results in slewed first impedance control signal V1 s. Second impedance control signal VD2 is slewed by a time constant provided by second timing resistor R2S and second timing capacitor C2, which results in slewed second impedance control signal V2 s. Third impedance control signal VD3 is slewed by a time constant provided by third timing resistor R3S and third timing capacitor C3, which results in slewed third impedance control signal V3 s. Control circuit 500 may be calibrated, at least in part, by making first, second and third timing resistors R1S, R2S, R3S and/or first, second and third timing capacitors C1, C2, C3 variable so they can be tuned. Control circuit may also be calibrated, at least in part, if thresholds Vth(a:n) are variable so they can be tuned. The time constants created in the control circuit should be faster than RC time constants formed in the subcells.

Z1(a:n) driver 510 comprises a driver for each increment/step in the impedance sequence. Components in Z1(a:n) driver 510 include Z1(a:n) comparator 511, Z1(a:n) driver 512 and Z1(a:n) inverted driver 513. In other words, in this embodiment of control circuit 500, if there are 10 steps there are ten drivers Z1(1) through Z1(10). The inputs to each Z1(a:n) comparator 511 consist of slewed first impedance control signal V1 s and a respective threshold Vth(a:n), which results in the output of each Z1(a:n) comparator providing a True output when slewed first impedance control signal V1 s exceeds the respective threshold Vth(a:n). The output of Z1(a:n) comparator 511 is driven by Z1(a:n) driver 512 as first variable series impedance control Vs1(a:n), which is provided to subcells Zs1 a through Zs1 n in first variable series impedance cell ZS1 c, as shown in FIG. 4. The output of Z1(a:n) comparator 511 is also driven by Z1(a:n) inverted driver 513 as first variable shunt impedance control Vp1(a:n), which is provided to subcells Zp1 a through Zp1 n in first variable shunt impedance cell ZP1 c, as shown in FIG. 4.

Z2(a:n) driver 515 comprises a driver for each increment/step in the impedance sequence. Components in Z2(a:n) driver 515 include Z2(a:n) comparator 516, Z2(a:n) driver 517 and Z2(a:n) inverted driver 518. The inputs to each Z2(a:n) comparator 512 consist of slewed second impedance control signal V2 s and a respective threshold Vth(a:n), which results in the output of each Z2(a:n) comparator providing a True output when slewed second impedance control signal V2 s exceeds the respective threshold Vth(a:n). The output of Z2(a:n) comparator 516 is driven by Z2(a:n) driver 517 as second variable series impedance control Vp1(a:n), which is provided to subcells Zp1 a through Zp1 n in second variable series impedance cell ZS2 c, as shown in FIG. 4. The output of Z2(a:n) comparator 516 is also driven by Z2(a:n) inverted driver 518 as second variable shunt impedance control Vp2(a:n), which is provided to subcells Zp2 a through Zp2 n in second variable shunt impedance cell ZP2 c, as shown in FIG. 4. Z3(a:n) driver 520 comprises a driver for each increment/step in the impedance sequence. Components in Z3(a:n) driver 520 include Z3(a:n) comparator 521 and Z3(a:n) driver 522. The inputs to each Z3(a:n) comparator 521 consist of slewed third impedance control signal V3 s and a respective threshold Vth(a:n), which results in the output of each Z3(a:n) comparator providing a True output when slewed third impedance control signal V3 s exceeds the respective threshold Vth(a:n). The output of Z3(a:n) comparator 521 is driven by Z3(a:n) driver 521 as third variable shunt impedance control Vp3(a:n), which is provided to subcells Zp3 a through Zp3 n in third variable shunt impedance cell ZP3 c, as shown in FIG. 4.

FIG. 6 illustrates an exemplary implementation of a control circuit in accordance with an embodiment of the invention. Control circuit 600 presents one of many possible embodiments to control cells, subcells and elements to provide impedance sequences for state transitions. Control circuit 600 may be used to control the exemplary constant impedance switch in FIG. 2, among other embodiments with appropriate scaling.

Control circuit 600 comprises decoder 605, first, second and third sequence timing 610, 615, 620, first through sixth multiplexer MUX1-6 and first through sixth drivers DRV1-6. As indicated in FIG. 6 by ellipses, a portion of control circuit 600 may be omitted. The portion missing depends on the number of steps in a sequence.

Decoder 605 receives state or state transition information in switch control signals V1 and V2, which may be provided, for example, by a switch controller or processor executing instructions. Decoder 605 decodes switch control signals V1, V2 into first, second and third impedance control signals VD1, VD2 and VD3. First impedance control signal VD1 is provided to first sequence timing 610, second impedance control signal VD2 is provided to second impedance timing 615 and third impedance control signal VD3 is provided to third impedance timing 620.

First impedance timing 610 creates a first impedance sequence of control signals Vd1(a)-(n) from first impedance control signal VD1. First impedance timing 610 creates a timing delay between each control signal in first impedance sequence of control signals Vd1(a)-(n). In this embodiment, the delay is created by a pair of inverters (i.e. a buffer) and a pair of RC circuits. For example, the delay between first impedance control signal VD1 and beginning first impedance sequence control signal Vd1(a) is created by first inverter Inv1, first RC pair R1 c, C1 c, second inverter Inv2 and second RC pair R2 c, C2 c and so on. The final delay between the second to last first impedance sequence control signal Vd1(n−1) and the last first impedance sequence control signal Vd1(n) is created by third inverter Inv2, third RC pair R3 c, C3 c, fourth inverter Inv4 and fourth RC pair R4 c, C4 c.

Second impedance timing 615 creates a second impedance sequence of control signals Vd2(a)-(n) from second impedance control signal VD2. Second impedance timing 615 creates a timing delay between each control signal in second impedance sequence of control signals Vd2(a)-(n). In this embodiment, the delay is created by a pair of inverters (i.e. a buffer) and a pair of RC circuits. For example, the delay between second impedance control signal VD2 and beginning second impedance sequence control signal Vd2(a) is created by fifth inverter Inv5, fifth RC pair R5 c, C5 c, sixth inverter Inv6 and sixth RC pair R6 c, C6 c and so on. The final delay between the second to last second impedance sequence control signal Vd2(n−1) and the last second impedance sequence control signal Vd2(n) is created by seventh inverter Inv7, seventh RC pair R7 c, C7 c, eight inverter Inv8 and eighth RC pair R8 c, C8 c.

Third impedance timing 615 creates a third impedance sequence of control signals Vd3(a)-(n) from first impedance control signal VD3. Third impedance timing 620 creates a timing delay between each control signal in the third impedance sequence of control signals Vd3(a)-(n). In this embodiment, the delay is created by a pair of inverters (i.e. a buffer) and a pair of RC circuits. For example, the delay between third impedance control signal VD3 and beginning third impedance sequence control signal Vd3(a) is created by ninth inverter Inv9, ninth RC pair R9 c, C9 c, tenth inverter Inv10 and tenth RC pair R10 c, C10 c and so on. The final delay between the second to last third impedance sequence control signal Vd3(n−1) and the last third impedance sequence control signal Vd3(n) is created by eleventh inverter Inv11, eleventh RC pair R11 c, C11 c, twelfth inverter Inv12 and twelfth RC pair R12 c, C12 c.

The timing delay between each control signal in first, second and third impedance sequences of control signals Vd1(a)-(n), Vd2(a)-(n) and Vd3(a)-(n) may be uniform or nonuniform. One or both resistor and capacitor in one or more RC pairs may be tunable to adjust delays between impedance sequence transitions, e.g. for correction or calibration in accordance with variations in process, temperature and voltage. Variable resistors and/or variable capacitors may be adjusted to adjust delays between impedance sequence transitions. In some embodiments, the respective values of resistors and capacitors in each RC pair may be unit values, i.e., the same value. It is notable that use of terms beginning, last, and terms in-between refer to a unidirectional sequence. In some embodiments, including the present one, sequences may be bi-directional, such that beginning and last may be reversed.

In the embodiment illustrated in FIG. 6, first, second and third impedance sequence control signals Vd1(a)-(n), Vd2(a)-(n) and Vd3(a)-(n) are provided as selectable inputs to multiplexers. More specifically, at least in this embodiment, the output of every other inverter, i.e. buffer, is an input to a multiplexer. The selected outputs of each multiplexer are provided as inputs to drivers. The impedance sequence control signals provide forward and reverse sequences to substantially maintain constant impedance for a plurality of switch events.

More specifically, first and second multiplexers MUX1, MUX2 receive first impedance sequence of control signals Vd1(a)-(n), third and fourth multiplexers MUX3, MUX4 receive second impedance sequence of control signals Vd2(a)-(n) and fifth and sixth multiplexers MUX5, MUX6 receive third impedance sequence of control signals Vd3(a)-(n). As indicated by ellipses, there may be additional multiplexers and drivers depending on the number of steps in the sequence. For example, if there are 10 steps in a sequence there are thirty multiplexers and drivers instead of six shown in FIG. 6, which only shows the first two for each set of impedances being controlled in the embodiment shown in FIG. 4.

As shown in this embodiment, first multiplexer MUX1 receives beginning first impedance sequence control signal Vd1(a) and last first impedance sequence control signal Vd1(n). First impedance control signal VD1 selects one of these impedance sequence control signals to activate or deactivate series and shunt unit impedances in the first step in a sequence for first variable series impedance cell ZS1 c and first variable shunt impedance cell ZP1 c depending on the switch event. As previously indicated, a switch event may call for a forward sequence or a reverse sequence.

First driver DRV1 drives the output of first multiplexer MUX1 as a pair of impedance control signals. In a forward sequence, first driver DRV1 drives a pair comprising first variable series impedance control Vs1(a) and first variable shunt impedance control Vp1(a), where first variable shunt impedance control Vp1(a) is inverted. In a reverse sequence, first driver DRV1 outputs a pair comprising first variable series impedance control Vs1(n) and first variable shunt impedance control Vp1(n), where first variable shunt impedance control Vp1(n) is inverted.

Second multiplexer MUX2 receives the next first impedance sequence control signal Vd1(a+1) and second to last first impedance sequence control signal Vd1(n−1). First impedance control signal VD1 selects one of these impedance sequence control signals to activate or deactivate series and shunt unit impedances in the second step in a sequence for first variable series impedance cell ZS1 c and first variable shunt impedance cell ZP1 c depending on the switch event calling for a forward or reverse sequence.

Second driver DRV2 drives the output of second multiplexer MUX2 as a pair of impedance control signals. In a forward sequence, second driver DRV2 drives a pair comprising next first variable series impedance control Vs1(a+1) and next first variable shunt impedance control Vp1(a+1), where next first variable shunt impedance control Vp1(a+1) is inverted. In a reverse sequence, second driver DRV2 outputs a pair comprising second to last first variable series impedance control Vs1(n−1) and second to last first variable shunt impedance control Vp1(n−1), where second to last first variable shunt impedance control Vp1(n−1) is inverted. As indicated, there may be additional multiplexers and drivers depending on the number of steps in the impedance sequence.

Third multiplexer MUX3 receives beginning second impedance sequence control signal Vd2(a) and last second impedance sequence control signal Vd2(n). Second impedance control signal VD2 selects one of these impedance sequence control signals to activate or deactivate series and shunt unit impedances in the first step in a sequence for second variable series impedance cell ZS2 c and second variable shunt impedance cell ZP2 c depending on the switch event. As previously indicated, a switch event may call for a forward sequence or a reverse sequence.

Third driver DRV3 drives the output of third multiplexer MUX3 as a pair of impedance control signals. In a forward sequence, third driver DRV3 drives a pair comprising second variable series impedance control Vs2(a) and second variable shunt impedance control Vp2(a), where second variable shunt impedance control Vp2(a) is inverted. In a reverse sequence, third driver DRV3 outputs a pair comprising second variable series impedance control Vs2(n) and second variable shunt impedance control Vp2(n), where second variable shunt impedance control Vp2(n) is inverted.

Fourth multiplexer MUX4 receives the next second impedance sequence control signal Vd2(a+1) and second to last second impedance sequence control signal Vd2(n−1). Second impedance control signal VD2 selects one of these impedance sequence control signals to activate or deactivate series and shunt unit impedances in the second step in a sequence for second variable series impedance cell ZS2 c and second variable shunt impedance cell ZP2 c depending on the switch event calling for a forward or reverse sequence.

Fourth driver DRV4 drives the output of fourth multiplexer MUX4 as a pair of impedance control signals. In a forward sequence, fourth driver DRV4 drives a pair comprising next second variable series impedance control Vs2(a+1) and next second variable shunt impedance control Vp2(a+1), where next second variable shunt impedance control Vp2(a+1) is inverted. In a reverse sequence, fourth driver DRV4 outputs a pair comprising second to last second variable series impedance control Vs2(n−1) and second to last second variable shunt impedance control Vp2(n−1), where second to last second variable shunt impedance control Vp2(n−1) is inverted. As indicated, there may be additional multiplexers and drivers depending on the number of steps in the impedance sequence.

Fifth multiplexer MUX5 receives beginning third impedance sequence control signal Vd3(a) and last third impedance sequence control signal Vd3(n). Third impedance control signal VD3 selects one of these impedance sequence control signals to activate or deactivate series and shunt unit impedances in the first step in a sequence for third variable series impedance cell ZS3 c and third variable shunt impedance cell ZP3 c depending on the switch event. Note that the embodiment in FIG. 4 does not have a third variable series impedance cell ZS3 c. As previously indicated, a switch event may call for a forward sequence or a reverse sequence.

Fifth driver DRV5 drives the output of fifth multiplexer MUX5 as a pair of impedance control signals. In a forward sequence, fifth driver DRV5 drives a pair comprising third variable series impedance control Vs3(a) and third variable shunt impedance control Vp3(a), where third variable shunt impedance control Vp3(a) is inverted. In a reverse sequence, fifth driver DRV5 outputs a pair comprising third variable series impedance control Vs3(n) and third variable shunt impedance control Vp3(n), where third variable shunt impedance control Vp3(n) is inverted.

Sixth multiplexer MUX6 receives the next third impedance sequence control signal Vd3(a+1) and second to last third impedance sequence control signal Vd3(n−1). Third impedance control signal VD3 selects one of these impedance sequence control signals to activate or deactivate series and shunt unit impedances in the second step in a sequence for third variable series impedance cell ZS3 c and third variable shunt impedance cell ZP3 c depending on the switch event calling for a forward or reverse sequence.

Sixth driver DRV6 drives the output of sixth multiplexer MUX6 as a pair of impedance control signals. In a forward sequence, sixth driver DRV6 drives a pair comprising next third variable series impedance control Vs3(a+1) and next third variable shunt impedance control Vp3(a+1), where next third variable shunt impedance control Vp3(a+1) is inverted. In a reverse sequence, sixth driver DRV6 outputs a pair comprising second to last third variable series impedance control Vs3(n−1) and third variable shunt impedance control Vp3(n−1), where second to last third variable shunt impedance control Vp3(n−1) is inverted. As indicated, there may be additional multiplexers and drivers depending on the number of steps in the impedance sequence.

The outputs of first through sixth drivers, i.e., impedance control signals Vs1(a:n), Vs2(a:n), Vp1(a:n), Vp2(a:n) and Vp3(a:n), are provided to respective subcells as shown in FIG. 4 to variously generate forward and reverse impedance sequences called for by particular switch events.

FIG. 7 illustrates a block diagram of an exemplary constant impedance single pole double throw second order switch with a plurality of variable impedances configured to provide constant impedance in accordance with an embodiment of the invention. Switch 700 is a second order embodiment, as compared to the first order embodiment in FIG. 3. Switch 700 may provide better isolation than switch 300. The impedance of switch 700 looking into first port RF1 is given by first port impedance Z1. The impedance of switch 700 looking into second port RF2 is given by second port impedance Z2. The impedance of switch 700 looking into third port RF3 is given by third port impedance Z3. A design and operation objective is to control each variable impedance ZS1A, ZP1A, ZS1B, ZP1B, ZS2A, ZP2A. ZS2B, ZP2B, ZP3 to substantially maintain each port impedance Z1, Z2 and Z3 at system characteristic impedance Zo during both static states and dynamic conditions (transitions) between states.

Determining how to control each impedance ZS1A, ZP1A, ZS1B, ZP1B, ZS2A, ZP2A. ZS2B, ZP2B, ZP3 to maintain impedance at each port RF1, RF2 and RFCOM requires impedance analyses to solve for variables. When characteristic impedance Zo is the same for each port RF1, RF2 and RFCOM, the number of static states and dynamic conditions may be reduced due to symmetry. Static states can be reduced to two states: an open (OFF) state and a path (either path) ON state. Dynamic conditions can also be reduced to two conditions: switching between an OFF state and a path ON state and switching between path ON states (i.e. from first path ON, second path OFF state to first path OFF, second path ON state and vice versa).

In a first dynamic condition when switching between an OFF state and a path ON state, one or the other of the first and second paths will be OFF, which means one of first set of variable series impedances Zs1 a, Zs1 b in the first path and second set of variable impedances Zs2 a, Zs2 b in the second path are deemed infinite (open circuit). For purposes of calculations, assume the first path is ON and the second path is OFF, which would mean for purposes of calculations that second set of variable series impedances Zs2 a, Zs2 b are an ideal high impedance. With second set of variable series impedances Zs2 a, Zs2 b open, second set of variable series impedances Zs2 a, Zs2 b and second set of variable shunt impedances Zp2 a, Zp2 b are irrelevant to the calculation of first and third port impedances Z1 and Z3. First port impedance Z1 is given by Equation 1:

Z ₁={[[(Z _(p3) ∥Z _(o))+Z _(s1b) ]∥Z _(1pb) ]+Z _(s1a) }∥Z _(p1a)   Equation 9

When second set of variable series impedance Zs2 a, Zs2 b are open, second port impedance Z2 equals characteristic impedance Zo. Thus, second port impedance Z2 is given by Equation 10:

Z₂=Z_(o)   Equation 10

Given the remaining circuit comprising first set of variable series impedances Zs1 a, Zs1 b and first set of variable shunt impedances Zp1 a, Zp1 b and third variable shunt impedance Zp3, symmetry in this circuit means shunt impedances Zp1 a and Zp3 will be the same, as will first and third port impedances Z1 and Z3. Thus, third port impedance Z3 is given by Equation 11:

Z₃=Z₁   Equation 11

Characteristic impedance Zo is known since it is defined by the system that switch 600 is coupled to. Given that system characteristic impedance Zo is known, the remaining variables may be selected to maintain first and third port impedances Z1, Z3 at characteristic impedance Zo by solving Equation 9 as shown in Equation 12:

Z _(p1a) ²(Z _(o) ² +Z ₀ Z _(s1b) −Z _(p1b) Z _(s1b) −Z _(p1b) Z _(s1a) −Z _(o) Z _(s1a) −Z _(s1a) Z _(s1b))+Z_(p1a)(Z_(o) ² Z _(p1b)+2Z _(o) ² Z _(s1b) +Z _(o) ² Z _(p1b) +Z _(o) ² Z _(s1a))+(Z _(o) ² Z _(p1b) Z _(s1a)+2Z _(o) ² Z _(s1a) Z _(s1b))=0   Equation 12

The quadratic formula in Equation 12 may be used to solve for first variable shunt impedance Zp1 a by selecting values for characteristic impedance Zo, first variable shunt impedance Zp1 b and first set of variable series impedances Zs1 a and Zs1 b. The results found in this first dynamic condition may be used to solve equations in the second dynamic condition.

In the second dynamic condition when switching between path ON states (i.e. from first path ON, second path OFF state to first path OFF, second path ON state and vice versa), third variable shunt impedance Zp3 is infinite (open circuit). First port impedance Z1 is given by Equation 13, second port impedance Z2 is given by Equation 14 and third port impedance Z3 is given by Equation 15:

Z ₁={[((Z _(o) ∥Z _(p2a) +Z _(sSa))∥Z _(p2b) +Z _(s2b))∥Z _(o) ∥Z _(p3) +Z _(s1b) ]∥Z _(p1b) +Z _(s1a) }∥Z _(p1a)   Equation 13

Z ₂={[((Z _(o) ∥Z _(p1a) +Z _(s1a))∥Z _(p1b) +Z _(s1b))∥Z _(o) ∥Z _(p3) +Z _(s2b) ]∥Z _(p2b) +Z2b}∥Z _(p2a)   Equation 14

Z ₃=[(Z _(o) ∥Z _(p1a) +Z _(s1a))∥Z _(p1b) +Z _(s1b)]∥[(Z _(o) ∥Z _(p2a) +Z _(s2a))∥Z _(p2b) +Z _(s2b) ]∥Z _(p3)   Equation 15

Equations 13-15 can be solved for any variable. In some embodiments, it may be desirable to ensure that the solutions for each transition utilize the same set of step values (albeit in different orders as needed to maintain port impedances) to minimize design, fabrication and operating costs. Other embodiments may employ different sets of step values for different transitions. However, for purposes of this embodiment, it will be presumed that the same set of step values will be used for all transitions (in different orders as needed to maintain port impedances). The results found in the first dynamic condition may be used to solve equations in the second dynamic condition. Characteristic impedance Zo is known (e.g. 50Ω) since it is defined by the system switch 700 is coupled to.

Table 5 below shows a logarithmic step example to maintain first, second and third port impedances Z1, Z2, Z3 of switch 600 substantially (e.g. +/−10%) at 50Ω during a transition from a first path ON state, second path OFF state to second path ON state, first path OFF state. In the embodiment shown in Table 5, the log base for the A group of variable impedances is 5.6, the log base for the B group of variable impedances is 4.2 and the static ON impedance is 2.4Ω combining the ON impedance of both series impedances in a path. The number of steps η is 5. A test frequency is 4 GHz. High impedance for A group of shunt impedances is 15,003Ω. High impedance for B group of shunt impedances is 7,490Ω. High impedance for A group series impedances is 2,601Ω. High impedance for B group of series impedances is 5,201Ω.

TABLE 5 Logarithmic Impedance Steps for Path 1 ON to Path 2 ON η A x B x Z_(p1a) Z_(s1a) Z_(p1b) Z_(s1b) Z_(s2b) Z_(p2b) Z_(s2a) Z_(p2a) 15003 0.8 7489.6 1.6 5201.1 2.3 2600.6 51.5 1 5.6 4.2 668.5 4.5 716.9 6.7 497.9 9.7 786.8 54.7 2 31.4 17.6 158.8 25.1 170.7 28.2 118.5 40.6 140.5 73.9 3 175.6 74.1 73.9 140.5 40.6 118.5 28.2 170.7 25.1 158.8 4 983.4 311.2 54.7 786.8 9.7 497.9 6.7 716.9 4.5 668.5 5 5507.3 1306.9 41.5 2600.6 2.3 5201.1 1.6 7489.6 0.8 15003

The sets of step values (step sequences) in Table 5 are reusable for other state transitions of switch 600 in the order justified by the transition. Due to symmetry, the step sequences may be reversed for reverse state transitions to maintain first, second and third port impedances Z1, Z2, Z3 of switch 600 substantially at 50Ω. In the embodiment shown in Table 5, first, second and third port impedances Z1, Z2, Z3 were maintained at 49 to 52Ω during each transition, which is less than 5% variation.

Table 6 provides additional implementation details for the exemplary embodiment presented in FIG. 6 with respect to the sequences provided in Table 5 to transition from the path 1 ON, path 2 OFF state to the path 1 OFF, path 2 ON state. In this embodiment, the transistor stack height in every variable impedance is four, except the A group of series impedances, each of which had a stack height of two. The stack height reduction for the A group of series impedances nearest first and second ports RF1, RF2 may help reduce insertion loss while still being able to handle power and provide sufficient isolation. This embodiment was implemented as an absorptive switch with a 25Ω resistor in series with an inductor coupling each shunt cell or subcell to ground. The corner frequency f_(o) is 2 MHz and unit Oxide capacitance is 1.84 pF/mm. Resulting switch time is 700 ns and VSWR is 1.26:1 to 1.38:1 depending on which port is being driven and the state transition. Of course, other embodiments may have the same or different parameters and results. The switching speed is given by an RC time constant in Equation 8. As with Table 4, Table 6 shows the width of transistors that are being turned ON or turned OFF in their respective sequences. A sequence of widths that begins with OFF lists transistors having those widths being turned ON in the order provided while a sequence that ends with OFF lists transistors having those widths being turned OFF in the order provided.

TABLE 6 Subcell Design for Logarithmic Impedance Step for Path 1 ON to Path 2 ON η W_(pa)(mm) R_(Gpa)(Ω) W_(sa)(mm) R_(Gsa)(Ω) W_(pb)(mm) R_(Gpb)(Ω) W_(sb)(mm) R_(Gsb)(Ω) OFF 1.47857 29,250 OFF 1.37143 31,535 1 0.00448 9,662,706 0.26403 163,802 0.00402 10,766,126 0.32653 132,449 2 0.01704 2,537,471 0.04715 917,289 0.01285 3,364,414 0.07775 556,285 3 0.03742 1,155,687 0.00842 5,136,817 0.05399 801,051 0.01851 2,336,399 4 0.03805 1,136,703 0.00128 33,878,840 0.22576 190,725 0.00523 8,267,909 5 0.01189 3,637,355 OFF 0.95238 45,411 OFF

While the configuration of switch 700 and sequences in Table 6 permit sequence control such that one subcell or element is turned on or off in each step, resulting in all subcells or elements being on or off at the end of a sequence, other embodiments may employ the same or different configurations of cells, subcells, elements and coding to control impedance sequencing during switching. Accomplishing the sequence of impedance steps may be accomplished by many different configurations of elements, subcells and cells. In other embodiments, cells, subcells and elements may be configured for and controlled by thermometer, binary, hybrid or other coding techniques to assemble and disassemble impedances in each step of a sequence. Impedances may be the same or different in each cell and/or subcell.

The foregoing equations for a multi-order constant impedance switch, actually any set of equations for a particular constant impedance switch, can be solved by a switch design calculator, which may be implemented as software instructions stored on a computer-readable storage medium and executed by a computer processor. Such a calculator can simultaneously, including iteratively, solve (e.g. try to find an optimal value) for each variable impedance based on a selected design parameters provided to the calculator, such as one or more of impedance step range, resolution, switch time, impedance type or implementation, number of steps, characteristic impedance, log base, insertion loss, isolation. The calculator can solve for one, several or all state transitions for a particular switch.

There are numerous advantages to substantially maintaining first, second and port impedances Z1, Z2, Z3 at characteristic impedance Zo during each of its transitions. By maintaining switch impedance during transitions, VSWR remains at or near 1:1, impedance spikes and reflections are eliminated, switching time may be reduced, operations can continue without delay and there is no need to design, fabricate and operate complex circuitry and programming to contend with impedance spikes and reflections.

Embodiments of the invention may be implemented as methods. One such method is illustrated in FIG. 8. FIG. 8 illustrates an exemplary method in accordance with an embodiment of the invention. No order of steps is required unless expressly indicated or inherently required. There is no requirement that an embodiment implement all of the steps illustrated in FIG. 8. FIG. 8 is simply one of many possible embodiments. Embodiments may implement fewer, more or different steps.

Method 800 comprises step 805, designing or configuring a switch having first and second port impedances, first and second states and first and second variable impedances. For example, as shown and discussed with respect to FIGS. 1-3, a designer or fabricator would select switch parameters based on specifications, such as the number of poles, throws, power, operating frequency, isolation, insertion loss, types of impedance elements, etc.

Method 800 further comprises step 810, determining first and second sequences of impedance values to step the first and second variable impedances through to maintain the first and second port impedances during one or more state transitions. For example, as shown and discussed with respect to FIGS. 3-6 and Tables 1-6, a designer would determine and a manufacturer and/or end-user would configure variable impedance sequences to substantially maintain port impedances at characteristic impedances during one or more transitions.

Method 800 further comprises step 815, calibrate the switch to maintain the first and second port impedances. For example, as shown and discussed with respect to FIG. 5, a manufacturer or end-user may calibrate a constant impedance switch. One of many possible calibration techniques comprises calibrating the RC time constant that slews impedance control signals. Another calibration technique comprises calibrating thresholds. Calibration may be done manually or automatically by a manufacturer, an end user, a switch control circuit, software, etc.

Method 800 further comprises step 820, operating the switch to maintain the first and second port impedances. For example, step 800 may be implemented by operating control circuit 500 and switch 400 in accordance with steps 825-840.

Method 800 further comprises step 825, determining whether there is a state transition (switch event). For example, logic in decoder 505 determines whether first and second switch control signals V1, V2 indicate switch 400 is transitioning between states. If not, then switch control 500 waits for a state transition by looping step 825. If there is a state transition, then method 800 proceeds to step 830

Method 800 further comprises step 830, determining starting and ending states in response to the state transition. For example, first and second switch control signals V1, V2 may indicate a state or a transition between states. If first and second switch control signals V1, V2 indicate a state then decoder 505 may store previous/existing states and determine a state transition by comparison to a state indicated by first and second switch control signals V1, V2. The starting and ending states may result in different sets of impedance control signals V1, V2, V3.

Method 800 further comprises step 835, issuing or receiving a sequence of signals to step the first and second variable impedances through first and second sequences of impedance values to maintain the first and second port impedances during the state transition between the starting and ending states. For example, Z1, Z2 and Z3 drivers in control circuit 500 may issue and switch 400 may receive a sequence of signals Vs1 a-Vs1 n, Vp1 a-Vp1 n, Vs2 a-Vs2 n, Vp2 a-Vp2 n, Vp2 a-Vp3 n to step respective variable impedance cells or subcells therein, such as first variable series impedance cell Zs1 c, first variable shunt impedance cell Zp1 c, second variable series impedance cell Zs2 c, second variable shunt impedance cell Zp2 c and third variable shunt impedance cell Zp3 c.

Method 800 further comprises step 840, stepping the first and second variable impedances through the sequence of impedance values during the state transition in response to the sequence of signals. For example, in response to switch 400 receiving a sequence of signals Vs1 a-Vs1 n, Vp1 a-Vp1 n, Vs2 a-Vs2 n, Vp2 a-Vp2 n, Vp2 a-Vp3 n, subcells in first variable series impedance cell Zs1 c, first variable shunt impedance cell Zp1 c, second variable series impedance cell Zs2 c, second variable shunt impedance cell Zp2 c and/or third variable shunt impedance cell Zp3 c step these variable impedance cells through sequences of impedance values, such as those shown in Tables 2, 3 and 4. At the end of step 840, method 800 returns to step 825 to await another state transition.

Methods and apparatuses have been disclosed for a constant impedance switch where switch impedance is dynamically managed to eliminate or substantially reduce impedance glitches during switching events by stepping variable impedances through sequences of impedance values. Switch impedance may be maintained for single and multi-throw switches having variable impedances of any order. Each variable impedance may comprise one or more configurable transistor cells, subcells or elements controlled by thermometer, binary, hybrid or other coding technique.

There are performance advantages provided by embodiments of the disclosed technology relative to conventional technology. For example, without limitation, by maintaining switch impedance during transitions, VSWR remains at or near 1:1, impedance spikes and reflections are eliminated or substantially reduced, switching time may be maintained or reduced, operations can continue without delay and there is no need to design, fabricate and operate complex circuitry and programming to contend with impedance spikes and reflections.

Proper interpretation of subject matter described herein and claimed hereunder is limited to patentable subject matter under 35 U.S.C. §101. Subject matter described in and claimed based on this patent application is not intended to and does not encompass unpatentable subject matter. As described herein and claimed hereunder, a method is a process defined by 35 U.S.C. §101. As described herein and claimed hereunder, each of a circuit, device, apparatus, machine, system, computer, module, media and the like is a machine and/or manufacture defined by 35 U.S.C. §101.

A device (i.e., apparatus), as defined herein, is a machine or manufacture as defined by 35 U.S.C. §101. A device may comprise, for example but not limited to, a switch or any device having a switch, e.g., an amplifier, attenuator, digital step attenuator, intermediate frequency (IF) device, radio frequency (RF) device, wireless device, communications device, radio system, receiver, transmitter, transceiver, cellular base station equipment and other communications and wireless infrastructure equipment, etc. For example, embodiments of the invention can be implemented in one or more IF and RF stages of receivers, transmitters and transceivers. Devices may be digital, analog or a combination thereof. Digital devices may have one or a plurality of programming modes, e.g., serial, parallel, latched parallel, for a plurality of different programming and control implementations.

Devices may be digital, analog or a combination thereof. Devices may be implemented with any one or more semiconductor processes or semiconductor technology, including one or more of BJT, HBT, MOSFET, MESFET, CMOS, BiCMOS or other transconductor or transistor technology. Implementation with different technologies may require alternative configurations other than the configuration illustrated in embodiments presented herein, which is within the knowledge of one of ordinary skill. Devices may be implemented in any discrete or integrated circuit fabrication technology, including but not limited to Silicon-Germanium (SiGe) semiconductors or other semiconductors comprising other materials and alloys.

Techniques described herein may be implemented in hardware (digital and/or analog) or a combination of hardware, software and/or firmware. Techniques described herein may be implemented in one or more components. Embodiments of the invention may comprise computer program products comprising logic (e.g., in the form of program code or software as well as firmware) stored on any computer useable medium, which may be integrated in or separate from other components. Such program code, when executed in one or more processors, causes a device to operate as described herein. Devices in which embodiments may be implemented may include storage, such as storage drives, memory devices, and further types of computer-readable media.

Examples of such computer-readable media include, but are not limited to, a hard disk, a removable magnetic disk, a removable optical disk, flash memory cards, digital video disks, random access memories (RAMs), read only memories (ROM), and the like. In greater detail, examples of such computer-readable media include, but are not limited to, a hard disk associated with a hard disk drive, a removable magnetic disk, a removable optical disk (e.g., CDROMs, DVDs, etc.), zip disks, tapes, magnetic storage devices, MEMS (micro-electromechanical systems) storage, nanotechnology-based storage devices, as well as other media such as flash memory cards, digital video discs, RAM devices, ROM devices, and the like. Such computer-readable media may, for example, store computer program logic, e.g., program modules, comprising computer executable instructions that, when executed, provide and/or maintain one or more aspects of functionality described herein with reference to FIGS. 1-7, as well as any and all components, steps and functions therein and/or further embodiments of the present technology described herein.

While the disclosed technology has been described with respect to a limited number of embodiments, it should be understood that they have been presented by way of example only, and not limitation. It will be understood by those skilled in the relevant art(s) that the spirit and scope of the subject matter of the present application encompasses a wide variety of implementations, including various changes in form and details to disclosed embodiments.

Embodiments are not limited to the functional blocks, detailed examples, steps, order or the entirety of subject matter presented in the figures, which is why the figures are referred to as exemplary embodiments. An embodiment in a device, apparatus or machine may comprise any one or more features described herein in any configuration. An embodiment in a method may comprise any process described herein, in any order, with any number of steps, using any modality.

The exemplary appended claims encompass embodiments and features described herein, modifications and variations thereto as well as additional embodiments and features that fall within the true spirit and scope of this present invention. 

What is claimed:
 1. A device comprising: a switch configured to maintain switch impedance during switching by stepping a variable impedance through an impedance sequence during the switching, where the switching transitions between states of the switch.
 2. The device of claim 1, the switch comprising a multi-throw switch, wherein the switch comprises: a first path between first and third ports, the first path comprising a first variable impedance configured to be stepped through a first impedance sequence during switching; and a second path between second and third ports, the second path comprising a second variable impedance configured to be stepped through a second impedance sequence during switching.
 3. The device of claim 2, wherein a first range of the first impedance sequence is different from a second range of the second impedance sequence.
 4. The device of claim 2, wherein steps in the first impedance sequence are logarithmic.
 5. The device of claim 2, wherein the first variable impedance comprises a first series impedance and a first shunt impedance and the first impedance sequence comprises a first series impedance sequence and a first shunt impedance sequence; the second variable impedance comprises a second series impedance and a second shunt impedance and the second impedance sequence comprises a second series impedance sequence and a second shunt impedance sequence; and the switch further comprises: a third variable impedance coupled between the first and second paths, the third impedance configured to be stepped through a third impedance sequence during switching.
 6. The device of claim 2, wherein the first and second variable impedances comprise, respectively, first and second configurable transistor cells.
 7. The device of claim 6, wherein the first and second configurable transistor cells comprise, respectively, a first and second circuit of selectable transistors selectable to provide the first and second impedance sequences during switching.
 8. The device of claim 8, wherein each selectable transistor in the first and second circuit of selectable transistors comprises a stack of transistors.
 9. The device of claim 2, the switching comprising a plurality of switching events, the switch further comprising: a control circuit that steps the first and second variable impedances, respectively, through the first and second impedance sequences during a first switching event and through additional impedance sequences for additional switching events to maintain switch impedance during the plurality of switching events.
 10. A method comprising: maintaining at least one impedance of a switch during a first switch event by stepping at least one variable impedance in the switch through a sequence of impedance values.
 11. The method of claim 10, the at least one variable impedance comprising first and second variable impedances, wherein maintaining the at least one impedance comprises: maintaining at least one impedance of the switch during the first switch event by stepping the first and second variable impedances, respectively, through first and second sequences of impedance values.
 12. The method of claim 11, further comprising: maintaining at least one impedance of the switch during a second switch event by stepping the first and second variable impedances, respectively, through third and fourth sequences of impedance values.
 13. The method of claim 11, wherein stepping the at least one variable impedance through a sequence of impedance values comprises: stepping the first and second variable impedances, respectively, through first and second logarithmic sequences of impedance values.
 14. The method of claim 11, wherein stepping the first and second variable impedances comprises: stepping a series variable impedance and a shunt variable impedance in a first path between first and second ports of the switch.
 15. The method of claim 11, wherein stepping the first and second variable impedances, respectively, through first and second sequences of impedance values comprises: stepping the first variable impedance through first sequence of impedance values having a first range; and stepping the second variable impedance through second sequence of impedance values having a second range, the first and second ranges being different.
 16. The method of claim 10, the at least one variable impedance comprising a first series variable impedance and a first shunt variable impedance in a first path between first and third ports of the switch, a second series variable impedance and a second shunt variable impedance in a second path between second and third ports of the switch and a third shunt variable impedance coupled to the third port, wherein the method comprises: maintaining impedances at the first, second and third ports of the switch during the first switch event by: stepping at least two of: the first and second series variable impedances and first, second and third shunt variable impedances, through at least two sequences of impedance values.
 17. The method of claim 11, the first and second variable impedances respectively comprising first and second configurable transistor cells, wherein maintaining the at least one method comprises: selecting transistors in the first and second configurable transistor cells during the first switch event to generate the first and second sequences of impedance values.
 18. The method of claim 10, further comprising: generating a sequence of control signals to step the at least one variable impedance through the sequence of impedance values.
 19. The method of claim 10, further comprising: calibrating the at least one impedance of the switch during the first switch event by adjusting at least one time interval between steps in the sequence.
 20. A method comprising: determining, by a processor, first and second sequences of impedance values to step, respectively, first and second variable impedances in a switch during switching to maintain at least one impedance of the switch during the switching. 